Session 1869-70.

Sixth Meeting, April 8, 1870.

W. Lassell, Esq., F.R.S., President, in the chair. Secretaries-Mr. Huggins, F.R.S., and Mr. Stone, F.R.S. The Minutes of the last meeting were read and confirmed. Thirty-seven presents were announced, and the thanks of the Society given to the respective donors.

Lieut. W. de Abney,

R. Abbay, Esq.,
Wm. T. Bayne, Esq.,

C. J. Lambert, Esq.,

E. H. Riches, Esq., LL.D.,
G. M. Seabrooke, Esq., and

Herbert Tomlinson, Esq.,

were balloted for and duly elected Fellows of the Society. The following papers were announced and partly read :—-On the Orbit of the Comet of 1683: by Mr. Plummer.

The comet was first seen by Flamsteed on the 3rd July, who observed it up to the 1st September. It was also observed by Hevelius. From the observations of Flamsteed an orbit was calculated by Halley, which was parabolic in form and of which the elements were given. In a recent number of the Astronomische

Nachrichten, Claussen, the Director of the Dorpat Observatory, has published the elements of an elliptic orbit, which he has deduced from the observations. The period given is 189.7 years, and the return to perihelion might therefore be expected in 1873. Mr. Plummer, at Mr. Hind's suggestion, has recalculated the orbit, making all possible corrections, and using the most recently obtained places for the stars of comparison, and finds a parabolic orbit represents the observations much better than any other, so that a return of the comet in a few years is not to be looked for. The observations of Hevelius were also rigorously reduced, but they were not equal to those by Flamsteed.

Observations of the Lunar Eclipse on January 17, 1870: by Mr. Tebbutt, jun.

The eclipse was remarkably well seen in New South Wales. At the commencement a thin filmy cloud covered the moon, but it soon disappeared, and the sky remained unclouded afterwards during the eclipse. Local mean times of the contacts and various phases were given, but these are obviously very difficult to fix. During the totality the shadow assumed a light copper-coloured tint, except at the edges of the disc, where it became green. The details of the lunar surface were quite perceptible in the dark shadow. Several telescopic stars were seen near the moon which it was evident would be occulted during the eclipse. This accordingly happened, and the times of several such occultations were given. The copper and green tints remained after the total phase was over. The telescope employed was a refractor of 34-inches aperture, 48 inches focal length, and power 30.

Capt. Noble enquired how the contact of shadows could be given to seconds as Mr. Tebbutt did?

Mr. Stone replied that Mr. T. only said they were noted as well as possible.

Capt. Noble: If they are within 30 seconds, it is as much as could be done.

On the Floor of Plato: by Mr. Birt.

In a paper read last November, the author showed the degree of visibility of the spots on this part of the moon's surface. The spots were then 25 in number, and the table referred to 16 of these. Continuing the subject, the author had now to state that 35 spots were now known (a diagram being exhibited), of which 8 had been discovered since November 27, 1869, in the course of 531 observations made since that date. The paper contained a table of the degree of visibility of the spots for the first 6 lunations of a year, for the second 6 lunations, the increase or decrease of each, and the average visibility for the year deduced from 771 observations. An increase had been found in 10 and a decrease in 11. Spot 3, which was a craterlet observed by Mr.

Dawes, showed the greatest decrease, and spot 19 the most increase, the extent of variation being very irregular. In a few instances only were they equally affected. Numbers 2 and 18 show the same increase of visibility. The greatest number of spots was always seen about the time of full moon. On comparing the series in which no more than 7 spots were seen, it was found that 5 were constant, but the remaining 2 were not the same, but varied exceedingly; some of the most difficult spots having been found on these occasions. Another year's observations, at least, would be required to work out the subject.

Professor Pritchard enquired what telescopes had been used. Mr. Birt: They varied from 6 to 9-inches.

The President: Reflectors or refractors?

Mr. Birt: Both. The greater number of observations was made with Mr. Crossley's 9-inch refractor.

Studies of the frequency of Sun Spots and their connection with the Magnetic Declination: by Professor Wolf.

This paper was taken as read.

The President said that the next subject to be brought before the meeting was the Total Solar Eclipse of December 22nd. There was a probability that the Admiralty might furnish a ship, like the Himalaya in 1860, to take observers to the stations and bring them back, and it became very important to know how many were likely to go. The three principal points appeared to be Xeres (near Cadiz), Oran, and Syracuse. The first and last seemed most suitable for an English expedition, Oran being left to the French. The first and most important observations were those to be made with the spectroscope, and others would be the photographic operations, eye observations, and those with the polariscope. If the stations were confined to two in number, about 40 observers and assistants would be required, and he should be glad to receive offers to volunteer from any gentlemen present. The Council had determined to issue a circular to the Fellows, requesting those who entertained the question of going out to let them know what kind of astronomical work they were disposed to do.

The Astronomer-Royal said that, as an humble servant of the Government, but by no means in its confidence, he thought he might usefully open the discussion by pointing out the local circumstances of the case, so that it might be ascertained first how many observers could be calculated on as likely to join the expedition. The eclipse shadow first touched land on the coast of Portugal, but the earliest habitable station was Xeres. Next came Gibraltar, which was easily visited and contained much that was interesting. Then came Oran in Algeria, which might be fairly left to our excellent neighbours across the Channel, who

were never behind in matters of science; and then Sicily. The central line passed near Syracuse, but he had a preference for Catania, at the foot of Etna, which he knew to be an agreeable locality. The shadow then passed over a desolate part of Greece and finished at the Black Sea between Balaclava and Sevastapol. There was no knowing where individuals might choose to go, but having sounded the Government, he thought it could hardly be expected that any money would be voted, but should any ships be disposable about the time, the observers might get conveyed to Gibraltar or Oran. As to Syracuse, however desirable as offering the chance of a better atmosphere, he had great doubt. It was much further off, and it was too much to expect that the Spanish observers should be landed so long before and have to wait so long after the eclipse, while the vessel went to Sicily and back. The only alternative will be to send two vessels; one for Gibraltar, and another to Sicily. Looking to the season of the year, and the voyage over the Bay of Biscay, he was afraid there would not be many offer to go; but fortune favours the brave, and he could assure them that if they saw the eclipse they would be amply repaid. His information was very meagre at present, but he was sure nothing would be done until the probable numbers were ascertained. Let them make a distinct proposal to the Government, and then they would get a distinct answer. Turning to the nature of the subjects of observation, he must observe that the time was very short (about two minutes), and that this would tend to confine the energies of the observers to one direction. The general opinion seemed to be that the subject of greatest importance was the nature of the corona; and here he must advert to a matter personal to himself. He had seen it stated in a newspaper and elsewhere, in support of a theory that the corona was an atmospheric phenomenon, that he held that opinion; but in order to show that this was incorrect, he quoted some extracts from his lecture at Manchester in 1861, showing what was his idea at the time, viz., that though it was possible the corona might be due to something of the nature of an atmosphere reflecting light, that something must be at least as far off as the moon was, and not at all the atmosphere surrounding the earth. The observations made in India and America had thrown great doubt upon the result of the experiments as to the polarisation of the corona, and he was afraid much ignorance prevailed upon the subject of polarisation, and that the observers did not know what polarisation in a plane passing through the sun's centre meant. He thought, therefore, before the expedition left, it would be necessary to have a sort of Polarisation Academy, and the observers should submit to an examination as to their competency. He

would suggest Professor Stokes as the proper person to test these parties. Unless this were done he should distrust the observations of the class in question; and as the corona was a very important object at this eclipse, he hoped the matter would not be neglected. With respect to the weather prospects, it should be remembered that it was the time of the winter solstice. Upon this point, however, he had much pleasure in introducing Lieut. Brown of the Royal Artillery, who, from his experience at Gibraltar, could give authoritative information on the subject.

Lieut. Brown said he had been called upon rather unexpectedly, but he must say that if he had to select the time for an eclipse he could not desire a better one than the end of December for Gibraltar. From an experience of six winters there as a photographer, he was satisfied that there were few climates to compare with it. He always selected that season for his work, as the light, though not so intense as in summer, gave the most perfect definition. He was afraid to say more on this head, or they might be overrun with photographers. Xeres was also an excellent place. The expedition would be received with open arms at Gibraltar, and every assistance given to it. Should a Levanter set in, which was the only fear, they could adjourn to St. Roque or further inland. A hurricane or rain was very unusual at that time, and in the absence of such, the weather was sure to be very good.

Admiral Ommaney desired to confirm Lieutenant Brown's statement in every respect, and to say that he knew no climate so agreeable as that of Gibraltar in the winter. At Xeres also they would find plenty of accommodation, and a month might be spent very pleasantly in the neighbourhood, many objects of interest being there. The climate of Syracuse was by no means so good as that of the south of Spain, and he thought the accommodation would be defective. Lieut. Brown had carried on hi work zealously and creditably, and his opinion should be o great weight. It might not be generally known that there was a Spanish observatory at St. Fernando, about three miles from Cadiz.

Lieut. Brown said he had taken some steps towards setting up an observatory on a small scale at Gibraltar.

The President thanked Lieut. Brown for his valuable information, and said it was a surprise to hear such favourable accounts of the climate of Gibraltar, as it had generally been assumed that Sicily would have the better weather.

Admiral Ommaney: The climate of Gibraltar is the best in the world in winter.

The President: As to that of Xeres?

Lieut. Brown: I do not know so much about that. I think it is hardly so fine as ours.